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Shestakovo site of Western Siberia (Russia): Pedogenic features, humic substances and paleoenvironment reconstructions for last 20–25 ka
Quaternary International xxx (2015) 1e9
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Shestakovo site of Western Siberia (Russia): Pedogenic features, humic substances and paleoenvironment reconstructions for last 20e25 ka Maria Dergacheva a, b, *, Irina Fedeneva a, Natalia Bazhina a, Olga Nekrasova c, Vasiliy Zenin b a
Institute of Soil Science and Agrochemistry of Siberian Branch of Russian Academy of Sciences, Av. of Academician Lavrentiev 8/2, 630090 Novosibirsk, Russia Institute of Archaeology and Ethnography of Siberian Branch of Russian Academy of Sciences, Av. of Academician Lavrentiev 17, 630090 Novosibirsk, Russia c Ural Federal University named after the First President of Russia B. N. Yeltsin, Lenina St. 51, 620000 Yekaterinburg, Russia b
a r t i c l e i n f o
a b s t r a c t
Article history: Available online xxx
New data characterizing sediments of the Shestakovo-III section located in the southern part of the West Siberian plain have been obtained. The section reveals 9 m of strata in which a number of paleosols and pedogenic zones are identified on the basis of cumulative features of pedogenesis. Paleosols and pedogenic features reflect the pedogenic transformation of sediments in different environments during the late Karghinsk interval (W2), Sartan Glaciation (W3) and Holocene period. The lower part of the sediments at a depth of 7.5e8.5 m has radiocarbon dates from 25 to 18,000 years. The obtained characteristics of the composition, structure and properties of humic substances, as well as comparison with data obtained earlier by other methods of environmental reconstruction enable recognition of the environment at the southern margin of the West Siberia Plain during the last 20e25 ka in more detail. © 2015 Elsevier Ltd and INQUA. All rights reserved.
Keywords: Pedogenic features Pedohumus method Paleoenvironment Late Pleistocene Holocene Western Siberia
1. Introduction The Shestakovo site is widely known in connection with the findings of bones and complete skeletons of dinosaurs and other fauna of the Cretaceous period (Averianov et al., 2002; Leschinsky et al., 2003; Lopatin et al., 2015). It is also known for a cluster of mammoth fauna associated with archeological artefacts of Paleolithic age (Derevianko et al., 2000a,b; Zenin et al., 2000a; Zenin, 2002). However, the site is extremely interesting from the points of view of paleogeography and stratigraphy. The upper part of these deposits is related to Sartan glaciations and Holocene time. The great thickness of this part of strata and their almost undisturbed state allow tracking directions of paleoecological changes in detail, revealing even relatively short cold and warm periods. Deposits of the Shestakovo site have attracted attention of research of different scientific directions (Leschinsky, 1998; Derevianko et al., 1998, 2000a,b, 2002; Zenin et al., 2000a, b;
* Corresponding author. Institute of Soil Science and Agrochemistry of Siberian Branch of Russian Academy of Sciences, Lavrentieva St. 8, 630090 Novosibirsk, Russia. E-mail address: [email protected] (M. Dergacheva).
Kuzmin et al., 2000, 2001; Fedeneva et al., 2000; Vasil'ev, 2001; Vasil'ev et al., 2002; Fedeneva, 2003). Publications include the stratigraphy of the Shestakovo site, radiocarbon data, sporo-pollen spectra of single stratigraphic layers, finds of Mammoth bones, and data of archaeological investigations. The composition of these deposits has been studied and paleoecological conditions have been discussed. This information has been published only in Russian (Fedeneva et al., 2000; Fedeneva, 2003). The direction of the paleoenvironmental change during the period of deposit formation in the Shestakovo-III section has been established (Fedeneva, 2003). The lower part of deposits that, according to the published radiocarbon dates (Derevianko et al., 2000a,b), corresponds to the end of the Karginsk interval and the beginning of the Sartan cryochron was generated in the southern taiga and (or) northern forest-steppe. During the Sartan cryochron, three stages of glacier activation divided by warmer stages have been identified. In this period the landscapes varied from tundra to southern taiga. During the Holocene optimum, the characteristics of the environment were consistent with the conditions of steppe and were warmer than in modern times. Thus, the general trend of the environment change in the last 20e25 ka in southern West Siberia based on some pedogenic
http://dx.doi.org/10.1016/j.quaint.2015.10.087 1040-6182/© 2015 Elsevier Ltd and INQUA. All rights reserved.
Please cite this article in press as: Dergacheva, M., et al., Shestakovo site of Western Siberia (Russia): Pedogenic features, humic substances and paleoenvironment reconstructions for last 20e25 ka, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.10.087
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M. Dergacheva et al. / Quaternary International xxx (2015) 1e9
features of deposits has been revealed. This trend does not contradict the reconstructions based on other methods of paleogeography (Derevianko et al., 2000a,b; Zenin et al., 2000a,b), but it includes the characteristics of only relatively long stages of paleogeographical history of this period. However, the need to reduce the step on the time scale in solving various problems of stratigraphy and paleogeography is obvious. Application of the pedohumus method of paleoenvironmental diagnosis (Dergacheva, 1997, 1998a,b, 2003, 2008, 2012) allows for a more detailed reconstruction of the changes in the natural conditions and climate than is possible using the traditional set of pedogenesis features (particle size distribution changes with depth TOC pH, CaCO3 and other characteristics of the material composition of deposits). Recently, the team of authors has obtained new data on the Shestakovo site deposits that characterize them from the viewpoint of paleopedogenesis. Products of organo-mineral interaction such as humic acids and their ratios with other components of humus substances have been studied. It is this combination of pedogenic features that forms the basis of the pedohumus method. The purpose of this paper is to present the reconstruction of the environment during the last 20e25 ka based composition, structure, and properties of humic acids as well as their ratio with other components of humus.
constitutes the orographic barrier for humid air masses coming from the north-west and south-west. This leads to the presence of areas with individual climate characteristics and complex alternation of steppe and forest-steppe, and taiga landscapes (Agroclimatic resources …, 1973; Trofimov, 1975). The climate of the study area has the following quantitative parameters: average temperature is 0.3 C, the average July temperature is þ18 C, in January 18 C; the sum of active air temperatures (over þ10 C) is 1700 C per year, and the amount of positive temperatures of 2000e2100 C; the average annual temperature of the soil surface is not more than 1 C, negative temperatures penetrate to a depth of about 1 m; prevailing winds are southwest; annual precipitation 420e470 mm with minimum during the summer months; the air humidity varies between 75 and 80%; and snow depth is not more than 0.5 m (Handbook of climate …, 1965). Leached and podzolized chernozems (Haplic Сhernozems and Luvic Phaeozems) are predominant soils in the study area. They are characterized by a considerable thick humus horizon with a high accumulation of total organic carbon (TOC), good structure, heavy texture, neutral-slightly alkaline reaction (pH 7e8), the prevalence of calcium in the soil absorbing complex and the presence of carbonates in the lower horizons of the soil profile (Trofimov, 1975; Khmelev, 1989).
2. Objects and methods
2.2. Objects of investigation
2.1. Regions studied
The Shestakovo site deposits represent the end of Karginsk interval (W2), Sartan Glacial (W3), and Holocene. This is confirmed by published radiocarbon dates for the lower part of the section obtained on the basis of animal bones (Derevianko et al., 2000a,b; Zenin et al., 2000b) and by the AMS date of 4857 ± 87 NSKA GA 3854 at a depth of 120e130 cm on deposits of the Holocene optimum. Deposits of the Shestakovo site were exposed in the section Shestakovo-III and by a series of additional sections and were previously described in detail from positions of stratigraphy and archaeological stratification (Leschinsky, 1998; Derevianko et al., 2000a,b). The Shestakovo-III section exposes 9 m of sediments in total. The sediments cover the period from 25 ka up to present time. Thirteen stratigraphic layers were distinguished in the sediments, which from the archaeology standpoint were stratified into 25 layers (layer 21 in the Shestakovo-III section sediments was absent) (Fig. 2). Section III revealed the following sequence of layers (description is given from the viewpoint of morphological reflection of pedogenic processes; with depths in a sampling place measured from the surface). Layer 1 (0e0.25 m). Humus horizon of modern arable leached chernozem (Huplic Chernozem). In the upper part is lighter-gray with brownish tinge (10 YR 6/1), in lower e dark gray with a brownish tinge (10 YR 4/1); fine angular blocky-granular structure, clay loam, compact, with abundance of roots; gradual transition to an underlying layer, boundary is smooth. Layer 2 (0.25e0.60 m). It is a little lighter than overlying layer: light gray with brownish tinge (10 YR 5/1), fine angular blockygranular structure, clay loam, compact (a little more compact in comparison with layer 1); with abundance of roots; gradual transition, boundary is smooth. Layer 3 (0.60e0.90 m). Light-brown with gray tinge (7.5 YR 7/1); with nutty subangular blocky-granular structure, loam (clay loam), rather compact; with abundance of roots; abrupt transition, boundary is smooth. Layer 4 (0.90e2.15 m). Includes the dual Holocene pedocomplex. The upper paleosol is presented by the humus horizon (A)' (dark gray Y 5/1, uniform in color, loam, with angular blocky-nutty structure, compact) and subhorizon (AB)' (dark gray with brown
The Shestakovo site is situated on the right bank of the Kiya River in Kemerovo Region (55 540 N. 87 570 W) on southern margins of the West-Siberian Lowland (Fig. 1). The area under research is on a very weakly undulated flat plain with altitudes 150e200 m a.s,l. Watershed areas are broken by shallow ravines and valleys of small brooks and rivers. The Shestakovo location belongs to the zone of “insular” forest steppe. Kemerovo Region is located in the center of the Asian continent and is characterized by extreme continental climate. The region also has specific climatic features due to relief. A mountain system
Fig. 1. Location of the Shestakovo site (according to Derevianko et al. (2000a) with changes).
Please cite this article in press as: Dergacheva, M., et al., Shestakovo site of Western Siberia (Russia): Pedogenic features, humic substances and paleoenvironment reconstructions for last 20e25 ka, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.10.087
M. Dergacheva et al. / Quaternary International xxx (2015) 1e9
Fig. 2. . Deposits of the Shestakovo-III section (according to Derevianko et al (2000a) with changes).
tinge 10 YR 4/1), loam, with nutty subangular blocky structure, compact). In the lower paleosol remained the humus horizon (A)'' (dark gray with weak brownish tinge 10 YR 5/1, loam (clay loam), with coarse blocky structure), horizon (B)'' (light brown 10 YR 5/ 4) clay loam, rather compact, with nutty subangular blocky structure) and horizon (BC)'' (pale-yellow 5 Y 6/4) clay loam, compact, with nutty structure, fissured, with accumulation of carbonates (pseudomicellia); flow of humus matter on the courses of roots). Layer 5 (2.15e2.83 m). Alternation of sandy, sandy loam and loam sublayers; sandy sublayers are 2e5 cm, loam sublayers e 1e1.5 cm (in the upper part of the layer more thick, to 8 cm, sandy loam sublayer is allocated). The general color is pale-yellow (5 Y 6/ 4), sandy sublayers are a little darker. Loam deposits have nutty subangular blocky structure, with carbonate pseudomicellia. In the lower part of the layer there are grey tones, iron spots and darker (dark-brown) sublayers. Gradual transition, boundary is smooth. Layer 6 (2.83e2.95 m). Variously colored e pale-yellow clay with dark-brown (5 Y 5/4) loamy sublayers and lens, with nutty subangular blocky structure, porous, compact, courses of roots, carbonate pseudomicellia, iron spots are noticeable; gradual transition to underlying layer, boundary is smooth.
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Layer 7 (2.95e3.48 m). Pale-yellow with dark-brown tinge (5 Y 5/4), loam clay, with nutty-blocky structure, porous; compact, fissured; courses of roots are noticeable, in the upper part of the layer e carbonate pseudomicellia; gradual transition to an underlying layer, boundary is smooth. Layer 8 (3.48e3.93 m). Dark-pale-yellow (5 Y 5/4), clay loam (clay), with nutty (nutty-blocky) structure; compact, ductile; abundant manganese spots, roots, rare pseudomicellia; transition to an underlying layer is abrupt, boundary is irregular. Layer 9 (3.93e4.41 m). The main color is pale-yellow (5 Y 6/4), brown e dark-brown sublayers are noticeable, clay loam, with nutty subangular blocky; pseudomicellia is noticeable only in darkcolored sublayers; rather compact; rare manganese spots e in the upper part of the layer; gradual transition to an underlying layer, boundary is smooth. Layer 10 (4.41e4.88 m). Light-pale-yellow (5 Y 8/4), more uniform in coloring, than layer 9; clay loam, with nutty-blocky structure; rather compact; rare manganese and carbonate spots, lightbrown spots (to 3e5 mm); the lower boundary is irregular, with wedges 5e6 cm, transition is abrupt. Layer 11 (4.88e6.03 m). Pale-yellow (5 Y 6/4), variously colored, in the lower part of the layer there are gray tone in coloring, lightbrown thin sublayers with not clear borders; loam clay, with nutty subangular blocky structure, on sides of particles iron spots are noticeable; rather compact, fissured; carbonate pseudomicellia, manganese spots are noticeable; the lower boundary is irregular, with wedges 5e6 cm, transition is abrupt. Layer 12 (6.03e7.22 m). Variously colored, the main color is dark-pale-yellow (5 Y 4/4) with alternation of more and less darkcolored sublayers (light-pale-yellow (5 Y 8/4), pale-yellow (5 Y 6/4), dark-pale-yellow (5 Y 4/4), in the lower part of the layer there are gray tone in coloring; with nutty subangular blocky structure, loam; rather compact, manganese and iron spots and rusty sublayers are noticeable; the lower boundary is wavy and transition e gradual. Layer 13 (7.22e7.31 m). Pale-yellow (5 Y 6/4), loam, with nutty subangular blocky structure; compact; thin sandy (or sandy loam) sublayers are noticeable; rare manganese spots; transition is gradual. Layer 14 (7.31e7.45 m). Similar in morphological properties to layer 13, differs in higher quantity of small particles (loam clay); the lower boundary is wavy, crumpled and transition is abrupt on coloring. Layer 15 (7.45e7.59 m). Light gray with brown tinge (10 YR 5/1), clay; angular block-granular structure; rather compact; the lower boundary is wavy. Layer 16 (7.59e7.79 m). Dark-pale-yellow with brown tinge (5 Y 4/3), uniform in color, loam, with nutty subangular blocky structure; rather compact; rare sandy lenses, manganese spots, carbonate pseudomicellia are noticeable; gradual transition, boundary is smooth. Layer 17 (7.79e7.88 m). Differs from layer 16 in lighter color e pale-yellow with a brownish tinge (5 Y 6/3), according to other morphological characteristics it is similar to layer 16. Layer 18 (7.88e7.98 m). Dark-pale-yellow, loam, with nutty subangular blocky structure; less dense in comparison with layers 16e17; rare manganese spots; smooth boundary and abrupt transition. Layer 19 (7.98e8.08 m). Dark-pale-yellow (5 Y 4/3), loam clay, with nutty-blocky structure, compact; abundant manganese spots; gradual transition. Layer 20 (8.08e8.18 m). Differs from layer 19 in the large amount of manganese spots; the lower boundary is wavy and transition is abrupt.
Please cite this article in press as: Dergacheva, M., et al., Shestakovo site of Western Siberia (Russia): Pedogenic features, humic substances and paleoenvironment reconstructions for last 20e25 ka, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.10.087
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Layer 22 (8.18e8.34 m). Light-pale-yellow (5 Y 8/4), in middle part quite thick rusty crumpled sublayer is noticeable; loam clay, with nutty-blocky structure, compact; gradual transition to underlying layer, boundary is wavy. Layer 23 (8.34e8.64 m). Dark-pale-yellow (5 Y 4/4), loam, with nutty-blocky structure, rather compact; rare manganese and iron spots, carbonate pseudomicellia. Layer 24 (8.64e8.79 m). Differs from layer 23 in the large number of manganese spots; gradual transition to underlying layer, wavy lower boundary. Layer 25 (8.79e8.96 m). It is similar on properties to overlying layers; gray tones (5 Y 5/1), sandy loam. Thus, morphologically deposits of the Shestakovo-III section are layered sediments, non-uniform in color, particle size distribution, structure, density, presence of impurities, and pedogenic transformation degree.
2.3. Methods of analyses Ninety-eight samples were taken in Shestakovo-III section for analysis. Previously, the following parameters have been measured in these samples (Fedeneva et al., 2000; Fedeneva, 2003): particle size distribution, content of total organic carbon (TOC), carbonates and pH, and humus composition according to the methods of Russian Soil Science adapted to paleosols (Dergacheva, 1984; Dobrovolckiy and Dergacheva, 2012). The study of this section and interpretation of materials obtained from Shestakovo-III deposits were continued from the pedohumus method standpoint. Data characterizing the composition and properties of humic acids and their ratio with other components of humus were obtained. Zones of pedogenesis have been distinguished in the sediments on the basis of data generalizations. A zone of pedogenesis is a layer (horizon) with specific features and differing from over and underlying sediments. The zone is determined by a combination of pedogenic features formed under influence of unidirectional humus- and soil-forming processes. The level of pedogenic features can be different: they can be represented as a full soil profile, as a single diagnostic horizon or their combinations, and morphogenetic or other properties of soil, which are close quantitative parameters. In this work, diagnosis of conditions of paleosol period formation and reconstruction of paleoenvironment for the last 20e25 ka is conducted on the basis of the composition and properties of humic acids and their ratio to fulvic acids. Humic acids were extracted by the standard method. Calcium was removed the humic acids were extracted by 0.1 n NaOH and were precipitated by 2 n HCl. The precipitation was separated by centrifugation, re-dissolved and precipitated by 2 n HCl again. Treatment of humic acids either by 6 n HCl or the mix HCl þ HF for removal of ash elements was not carried out. The share of carbon in elemental composition of humic acids is most closely correlated with temperature conditions, the share of hydrogen is correlated with moisture conditions, and the ratio of these elements (H:C) has a close correlation with all major climatic indices (Dergacheva et al., 2012). The correlation coefficient ranges from 0.75 to 0.98. The element ratio of humic acids, color coefficient Е465:E665 (Welte, 1955) and the ratio of humic acids with fulvic acids are used for revealing paleosol forming conditions. These characteristics are closely correlated with the period of biological activity (PBA). According to Orlov (1990), the PBA duration is equal to the period during which the air temperature is consistently over 10 C and the moisture available is not less than 1e2%.
To visualize the results of the study of the system of paleosol humus substances, the graphic principles described previously (Dergacheva, 1984) have been used. Using humus profilegrams, one can present the features of humus substances composition in the form of areas that give visual representation of the changes of parameters of groups and fractions within the profile and presence of uniform and different thicknesses that can be identified as pedogenic zones. As diagnostics and reconstruction of paleoenvironment in this article are carried out using the pedohumus method, we briefly describe the most important of its provisions by which it is possible to use it as an independent method of paleogeography similar to the method of sporo-pollen analysis. First at all, the composition and properties of humic acids, as well as their ratio to the other components of humus substances, are caused by the specific conditions (the combination of temperature and humidity) in the place where they were formed (Dergacheva, 1997, 2008). Humic acids are accumulative component humus and they almost do not migrate. In addition, humic acids, as well as aggregate of humus substances, are self-regulating systems that can maintain status acquired during their formation (Dergacheva, 1989). The share of carbon in the humic acids of soils and paleosols depends on the zonal natural conditions and the continental climate. Key indicators of the elemental composition of humic acids paleosols do not depend on their age. They are caused by climate. Humic acids preserve of some properties in diagenesis during Pleistocene-Holocene period (Dergacheva et al., 2000, 2012). A detailed description of the method has a number of works only in Russian (Dergacheva, 1997, 1998a,b; 2008, 2011, 2012). The principles of the method and also the diagnostics and reconstruction paleoenvironment based for this method have been published in English as well (Dergacheva, 1998a, 2013, 2003; Fedeneva and Dergacheva, 2003, 2006; Dergacheva et al., 2012). 3. Results of investigation and their interpretation It has been shown (Fedeneva, 2003) that the mineral part of deposits transformed by a pedogenic processes is relatively monotonous especially in the lower part from 6 to 9 m. The greatest variation has been found in sand particles (Fig. 3). According to data (Fig. 3), the entire thickness of sediments is rich in calcium carbonate, varyimg mostly between 5 and 8% by weight of fine earth. Very high accumulation of calcium carbonate is found only in sediments associated with the humus layer of the Holocene optimum at the depth of 178e215 cm. While the mineral part of deposits is relatively monotonous, the quantitative and qualitative characteristics of organic matter vary in thickness substantially (Fig. 4). The content of organic carbon throughout the section, except for profiles of the modern soil and paleosol of Holocene optimum is less 0.3% of fine deposit mass (Fig. 4, a). The distribution of organic carbon throughout the section makes it possible to distinguish layers of relative humus accumulation. These layers are also characterized by increase in both the share of humic acids and in the carbon ratio of humic and fulvic acids (Cha:Cfa) (Fig. 4, b, i). Fulvic acids, as a rule, are prevailing forms among humus substances (Fig. 4, b). In some cases non-hydrolyzed forms of humus (humins) are dominant (Fig. 4, d). The content of humic acids reaches 30e40% in some layers (Fig. 4, b), that for paleosols and deposits of Late Neopleistocene can be estimated as relativity high (Dergacheva and Zykina, 1988). Calcium humates prevail among humic compounds (Fig. 4, f). Humic acids associated with clay minerals are in insignificant quantities. In some layers this form of humus substances is in trace quantities or is absent. The quantity of free fulvic acids
Please cite this article in press as: Dergacheva, M., et al., Shestakovo site of Western Siberia (Russia): Pedogenic features, humic substances and paleoenvironment reconstructions for last 20e25 ka, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.10.087
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Fig. 3. General characteristics of the deposits of the Shestakovo-III section: А e layers; B e particle size distribution (mm): 1e 1e0.25; 2 e 0.25e0.05; 3 e 0.05e0.01; 4 e 0.01e0.005; 5 e 0.005e0.001; 6 e <0.001; C ephysic-chemical properties.
(fraction 1a, according to Ponomareva and Plotnikova, 1980) slightly varies in most deposits, gradually decreasing to the upper 2 m (Fig. 4, h). Features of structure and properties of humic acids (H:C, C:N, E465:E650) also significantly vary in deposits, reflecting relative changes of the environment (Fig. 5, d, e, f). In deposits of the lower part of the section (from 9 to 7 m), the H:C ratio is within the range 1.3e1.4 (approximately), and nitrogen saturation of humic acids (C:N ratio) in the most cases is more than 14e15, being reduced to 11e12 in the upper part of the section. The value of the E465:E650 ratio characterizing complexity of humic acid structure (i.e., the ratio of their shears between the peripheral and so-called nuclear parts) is specific for the modern soils formed in humid conditions. The deposits correlating with the Sartan period of the Late Pleistocene differ in alternation of values of both H:C ratios in
humic acids and E465: E650. In general, their fluctuations are not beyond typical characteristics of HA under humid conditions. These features of HA indicate repeated changes of the relative cooling and warming, against the background of stable temperature conditions changes of humidity. Such specificity of climatic conditions is observed for sediments at a 700e225 cm. In the upper part, the combination of features of humic acids and their ratio to fulvic acids reveal a number of layers with humic acids corresponding to formation in warmer and in less humid conditions (in some cases even arid). The features of humic substances of the Holocene part deposit from 225 cm to the surface reveal a dual pedocomplex of the Holocene optimum and the set of modern soil horizons. The analysis of the set of pedogenic features of Shestakovo section deposits allow us to distinguish a number of pedogenic zones, which characterize different conditions of deposit formation and features of soil forming process (Fig. 5, a, b).
Please cite this article in press as: Dergacheva, M., et al., Shestakovo site of Western Siberia (Russia): Pedogenic features, humic substances and paleoenvironment reconstructions for last 20e25 ka, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.10.087
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Fig. 4. Humus profile of the Shestakovo III section deposits: a e TOC, % to soil mass; % to TOC: b e 3; h e FA, fraction 1a; i e Cha:Cfa.
P P HA; c e FA; d e Humin; e e HA, fraction 1; f e HA, fraction 2; g e HA, fraction
Fig. 5. Complex of deposit features of the Shestakovo -III section based on humus substance characteristics (A) and scheme of presence of layers and pedogenic zones (B) a e TOC, % to soil mass; b e magnetic susceptibility, c$105/kg SI; c e Cha:Cfa; Characteristics of humic acids: d e H:C; e e C:N; f e E465:E650.
All deposits were divided into 16 pedogenic zones (the first is in the lower part of Shestakovo section, the 16th e in its upper part). According to data in Figs. 4 and 5, the pedogenic zones have different characteristics. The analysis of quantitative characteristics of the 16 zones of pedogenesis showed that there were numerous changes in bioclimatic conditions over the last 20e25 ka. Diagnostics of pedogenesis conditions have been performed for each of the studied sample, taking into account that the formation of humic acids takes place in accordance with a combination of temperature and moisture; that they are an accumulative component of the soil, and that they are satisfactorily preserved in diagenesis (Dergacheva, 2008). The results were generalized for each zone of pedogenesis. Diagnosis was based on the relationships
between the parameters of humic acids and other humus characteristics of modern soils on the one hand, and with environmental conditions of their formation, on the other. Different indicators of the environmental state are used for this purpose. It is impossible to present the entire volume of diagnosed data and full description of the diagnostic procedure in the given article. We demonstrate the procedure with the example of determination of the period of biological activity, which depends on the combination of heat and moisture. For the analysis of pedogenic zones, the average data for each are used (Fig. 6). This procedure can be performed for the humus horizons or some individual samples depending on the problems being solved. The results demonstrated in Figs. 4e6 and their generalization (Table 1) have revealed the change of periods of
Please cite this article in press as: Dergacheva, M., et al., Shestakovo site of Western Siberia (Russia): Pedogenic features, humic substances and paleoenvironment reconstructions for last 20e25 ka, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.10.087
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Fig. 6. Calculation of the periods of biological activity (PBA) of the formation of paleosols and deposits overworked by pedogenesis of Shestakovo-III section using average data for pedogenic zones. IeXVI e pedogenic zones. It is based on the results of studying H:C of humic acids of modern soils formed under varying durations of PBA.
biological activity (PBA) during the formation of the deposits according to each zone of pedogenesis.
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Pedogenic zone II (770e825 cm) differs in the higher amount of organic carbon (0.24 ± 0.02) with small changes in depth, in the higher value of the magnetic susceptibility (1.5e2.0$105/kg), in the tendency to reduction share of humic acids in humus composition to a top of this pedogenic zone, and also slightly in the varying Cha:Cfa, and H:C ratios (0.71 ± 0.08 and 1.36 ± 0.05 respectively). The absolute values of saturation of humic acids by nitrogen and color coefficient tend to decrease. The last parameter has no statistically reliable difference from the previous layer. Sediments in this pedogenic zone were also formed on the background of high humidity, though relatively weaker than zone I. On average, the duration of the PBA is shorter (Fig. 6). Northern taiga replaced southern taiga. Pedogenic zone III includes deposits from 730 to 770 cm. According to the content of organic carbon (0.24 ± 0.03) these deposits does not practically differ from those in the previous zone by the lower content of humic acids, similar content of fulvic acids, significantly lower value of Cha:Cfa (on average 0.58 ± 0.11), similar H:C ratio values (1.37 ± 0.09), and more “mature” humic acid (E4:E6 ¼ 4.11 ± 0.22). During this period, the conditions were almost identical to the previous one. The deposits at the depth of 700e730 cm belong to pedogenic zone IV. This zone is distinguished on the basis of the increased magnetic susceptibility, relatively lower organic carbon content, and Cha:Cfa, and E4:E6 ratios. Its formation proceeded under con-
Table 1 Pedogenic zones of Shestakovo section Pedogenic zone
Depth, cm
TOC, % (average)
I II III IV V VI VII VIII IX X XI XII XIII XIV XV
825e900 770e825 730e770 700e730 595e700 545e595 490e545 425e490 390e425 340e390 275e340 240e275 195e240 140e195 90e140
0.17 0.24 0.24 0.19 0.15 0.18 0.17 0.17 0.16 0.18 0.25 0.12 0.21 0.63 1.90
XVI
0e90
2.17 ± 1.08
a b
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.05 0.02 0.03 0.02 0.01 0.02 0.01 0.02 0.02 0.02 0.03 0.03 0.04 0.33 0.53
Cha:Cfa (average) 0.68 0.71 0.58 0.49 0.34 0.56 0.81 0.60 0.65 0.55 0.93 0.33 0.36 1.06 2.29
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.28 0.08 0.11 0.05 0.08 0.14 0.24 0.15 0.19 0.10 0.18 0.07 0.04 0.67 0.36
1.39 ± 0.22
PBA for pedogenic zone, days
Landscape
PBA different landscape conditions, daysb
14
0.05 0.05 0.09 0.04 0.06 0.12 0.10 0.09 0.31 0.07 0.16 0.14 0.09 0.18 0.07
92 87 87 90 119 125 118 119 87 115 100 130 100 150 165
Southern taiga Northern taiga Northern taiga Northern Taiga Southern taiga Forest-steppe Southern taiga Southern taiga Northern taiga Southern taiga Southern taiga Forest-steppe Southern taiga Forest-steppe Steppe
90e120 60e90 60e90 60e90 90e120 120e150 90e120 90e120 60e90 90e120 90e120 120e150 90e120 120e150 150e180
from 18040 ± 175 to 24360 ± 150a
0.84 ± 0.04
150
The southern forest-steppe
150e180
H:C (average) 1.34 1.36 1.37 1.36 1.14 1.09 1.20 1.14 1.37 1.16 1.28 1.02 1.29 0.84 0.71
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
C dates
For depth 120e130 cm 4857 ± 87 (NSKA GA 3845) Modern period
According to Zenin et al. (2000b) According to Orlov (1990).
The first pedogenic zone is allocated at a depth of 825e900 cm and is characterized by gradual increase of several parameters from the lower part. They are: organic carbon (from 0.07 till 0.21), humic acids (as the tendency) and the value Cha:Cfa (from 0.48 to 1.10), reduction of a share of fulvic acids and saturations of humic acids by nitrogen. Ratios of H:C and E465:E650 (further in the text e E4:E6) change slightly. The first indicator on averages is 1.34 ± 0.05, the second is 4.73 ± 0.13 (Table 1). Here pedogenesis occurred under conditions of high humidity indicated by morphological features listed above, but also by the composition and properties of humic acids with parameters similar to modern soils of humid conditions of formation. The period of biological activity during the formation of the first pedogenic zone could be about 92 days, decreased to 87e90 days in zones IIeIV.
ditions in northern taiga but under relatively higher heat supply and lower humidity. Paleosols and sediments overworked by pedogenesis following pedogenic zones (VeVIII) were formed under more favourable conditions when the PBA varied around 120 days. The fifth zone of pedogenesis at 595e700 cm is characterized by lower values of TOC, magnetic susceptibility, the share of humic acids in the composition of humus substances, and Cha:Cfa value. Indicators H:C and Е4:Е6 point to the beginning of relative warming. The PBA was longer than about 20 days, and met the conditions of the southern taiga. The sixth zone of pedogenesis on the depth 545e595 cm shows further warming reflecting in the transformation of all features of humus in sediments changed by pedogenesis. Humic acids have
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M. Dergacheva et al. / Quaternary International xxx (2015) 1e9
relatively higher proportions of carbon in the elemental composition and the ‘nucleus’ portion in the structural organization. The PBA met the conditions of the forest-steppe (Table 1). The next seventh zone of pedogenesis (490e545 cm) occupies the second half of the eleventh layer and it is characterized by a very low magnetic susceptibility (less than 1.0$105/kg SI) that is specific for this section and by its slight fluctuation, which may indicate the influence of increased humidity. This zone of pedogenesis is very heterogeneous in a number of characteristics. The humic acids and their ratio to fulvic acids correspond to relatively warm and humid conditions. The content of humic acids points to the continuing relative warming that in general is confirmed by the values of H:C and Е4:Е6. The random thin interlayer (probably redeposited) divides these sediments into two parts with similar features. The average values of the composition and properties of humic substances of this zone were calculated without characteristics of this interlayer. The eighth pedogenic zone with thickness of 65 cm (425e360 cm) is close to the previous zone in the total organic carbon content (0.17 ± 0.02), higher magnetic susceptibility (1.12 ± 0.07), the increased amount of fulvic acids in the humus composition, and the value of H:C and Е4:Е6 of humic acids, corresponding to forest conditions with relatively cold and humid conditions. The PBA of this zone is 119 days and is nearly identical to the previous one. Then, there was a reduction of PBA to a minimum of about 87 days that was related with a significant cooling. The ninth zone of pedogenesis (390e425 cm) has low TOC, close to the values Cha:Cfa and Е4:Е6 to those of previous pedogenic zone and reflecting the same conditions. However, the lower ratio of C:N may indicates changes in the vegetation, affecting saturation of humic acid by nitrogen. In this zone, the differentiation of pedogenic characteristics in most strata is observed: the share of humic acids increases and fulvic acids decreases, and the absolute values Cha:Cfa increase from bottom to top. In accordance with these facts, the ratio of H:C is gradually lowered. In general, the sediments of this pedogenic zone correspond to relatively colder formation conditions than in the previous case. During the formation of the next pedogenic zone the PBA increased to 115 days, then during the formation of XI and XIII zones it was about 100 days, and during XII zone about 130 days. The tenth zone of pedogenesis includes deposits with thickness of 50 cm (from depth of 340 cm) with low TOC, low magnetic susceptibility and characteristics of humic acids corresponding to the southern forest type The higher amount of total organic carbon is observed in sediments of the eleventh pedogenic zone, but the combination of different features of the composition and properties of humic acids and their correlation with fulvic acids is variable. The interlayers with characteristics reflecting relatively warmer or colder wet conditions of pedogenesis alternate. The relative warming is reflected in the characteristics of sediments of the next, XII zone of pedogenesis, which is a dual pedocomplex consisting of superimposed paleosols. Probably rare and low-power lithogenesis dominated in this period, which was followed by transformation of soil formation processes. Both paleosols are very thin (no more than 15e20 cm), but the parameters of their humus horizons correspond to overall warming of the climate. The deposits of this zone were formed in forest-steppe. Properties of the pedogenic zone XIII reflect the next phase, which terminates the Sartan period. The following two zones of pedogenesis at the depth of 90e195 cm are the profiles of paleosols formed under warmest conditions. The value of PBA reflects the fact that this pedogenic zone was formed under southern taiga conditions. The upper of these zones was formed as the result of a rare
but powerful lithogenesis and its subsequent pedogenic transformation. The highest period of biological activity was during the formation of the upper paleosols of the pedocomplex of Holocene optimum. The conditions of formation of humus and soils were favorable and characterized by the highest PBA duration of 165 days. The durations of PBA of the lower paleosol of this pedocomplex and modern soil are almost identical. The humus horizon of the paleosol formed in warmer and drier conditions. In zone XIV at the depth of 140e195 cm is a chernozem paleosol with typical change in TOC with depth, change in the magnetic susceptibility, and the shares of humic acids and fulvic acids. The former decrease with depth, the latter increase, and characteristics of humic acids correspond to the level of the steppe soil. This soil is clearly differentiated into horizons (A), (AB) and (B) in all respects. There is another paleosol characterized as a zone XV. It was formed in steppe conditions and is differentiated into two horizons, (A) and (AB). Characteristics of humic acids correspond to steppe soils with different degrees of humidity. The zone of pedogenesis XVI has a thickness of 90 cm, has the horizons A, AB and B in this section, and corresponds to all the quantitative parameters of a Chernozem formed in the southern part of forest-steppe. Thus, one can diagnose the paleoenvironment with any step of timeline, with any amount and location of samples, conduct neighboring correlations, and compare identified general trends of changes in the environment of local areas. Instead of the H:C ratio and the relationship of this characteristic of humus composition with PBA, it is possible to use any indicator of composition, structure and properties of humic acids that is specific to the conditions of the environment and preserves their specificity in diagenesis. Any indicators of climate, vegetation, or relief can also be used in that case, if the current relationships are already identified. 4. Conclusion The approaches of pedohumus method to paleosol diagnostics and paleoreconstruction allowed detailed paleoenvironment reconstructions of the end of the Karginsk interstadial, the Sartan glacial period and the Holocene. A number of bioclimatic condition fluctuations caused by local specificity of the climate was revealed. It has been established that the lower part of the deposits formed in the final stages of the Karginsk interval or at the beginning of the Sartan period corresponds to conditions of taiga landscapes. The deposits of several pedogenic zones correspond to forest-steppe landscapes. The stages of glacier activation are distinguished during the Sartan period, which were interrupted by relatively warm stages. The landscapes varied in the range from northern taiga to forest-steppe within this period. The most prominent event of the Holocene was the climatic optimum during which a paleosol of chernozem type was formed and the environment corresponded to steppe conditions favourable for soil formation. Diagnostics conducted by pedohumus method does not contradict data obtained by palynological and other paleogeography methods (Derevianko et al., 2000a,b). The obtained characteristics of the composition, structure and properties of humic substances, as well as comparing the results of environment reconstruction by other methods have allowed us to carry out more detailed environment diagnosis of the last 20e25 ka on the West Siberian Plain's southern edge. Moreover, they have illustrated the reliability of information preserved in humic acid features. The formation of the deposits of the Shestakovo-III section happened during a change from frequent but weak lithogenesis to rare and weak and then (approximately from the depth of 225 cm) rare and powerful lithogenesis.
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Acknowledgments The necessary reconstruction data including characteristics of humus substances of Tuva region modern soils were obtained in Institute of Soil Science and Agrochemistry through support by Russian Fundamental Basic Research, project 14-04-32354. The study of the Ural region modern soil humic acids characteristics for the same purpose in the Ural Federal University was supported by Act 211, Government of the Russian Federation, contract N 02.A03.21.0006. References Agroclimatic Resources of Kemerovo Region, 1973. Gidrometeoizdat, Leningrad, 143 p. (in Russian). Averianov, A.O., Voronkevich, A.V., Maschenko, E.N., Leshchinskiy, S.V., Fayngertz, A.V., 2002. A sauropod foot from the Early Cretaceous of Western Siberia, Russia. Acta Palaeontologica Polonica 47, 117e124. Dergacheva, M.I., 1984. Organic Substance of Soils: Static and Dynamic. Nauka, Novosibirsk, 155 p. (in Russian). Dergacheva, M.I., 1989. System of Soil Humus Substances. Nauka, Siberian Branch Russian Academy of Sciences, Novosibirsk, 110 pp. (in Russian). Dergacheva, M.I., 1997. Archaeological Pedology. Siberian Branch, Russian Academy of Sciences, Novosibirsk, 231 p. (in Russian). Dergacheva, M.I., 1998a. New approaches to the reconstruction of environment of ancient men's inhabitation. In: Paleoecology of Pleistocene and Stone Age Cultures in Northern Asia and Adjacent Territories. Materials of International Symposium, vol. 1. Institute of Archaeology and Ethnography, Novosibirsk, Russia, pp. 78e82. Dergacheva, M.I., 1998b. Reconstruction of Soil Forming Conditions by Pedohumic Method. Ecology and Soils. Pushino, Russia, pp. 263e283 (in Russian). Dergacheva, M.I., 2003. Pedohumic method in paleoenvironmental reconstructions: an example from Middle Siberia. Quaternary International 106107, 73e78. Dergacheva, M.I., 2008. Humus as a Carrier of Soil Memory. Soil in Memory: Soil as a Memory of Biosphere-Geosphere-Anthroposphere Interactions. LKI Publishers, Moscow, pp. 530e560 (in Russian). Dergacheva, M.I., 2011. Humic substances as source of information about environment formation. Annals of Agrarian Science: Georgia 9 (2), 57e61 (in Russian). Dergacheva, M.I., 2012. Humic Substances as Keeper of Information about Ancient Pedogenesis. Paleosols, Environment and Their Diagnosis Method. Novosibirsk, pp. 61e75 (in Russian). Dergacheva, M.I., 2013. Pedohumic Method of Paleoenvironment Reconstruction Key Items and Their Illustration of Different an Example. Soils in Space and Time. Ulm: Germany, pp. 145e146. Dergacheva, M.I., Nekrasova, O.A., Okoneshnikova, M.V., Vasileva, D.I., Gavrilov, D.A., Ochur, K.O., Ondar, E.E., 2012. Ratio of elements in humic acids as a source of information on the environment of soil formation. Contemporary Problems of Ecology 5, 643e647. Dergacheva, M.I., Vashukevitch, N.V., Granina, N.I., 2000. Humus and HolocenePliocene Soil Formation in Predbaikalia. Siberian Branch Russian Academy of Sciences, Novosibirsk, p. 204 (in Russian). Dergacheva, M.I., Zykina, V.S., 1988. Organic Matter of Fossil Soils. Nauka Press, Novosibirsk, 129 p. (in Russian). Derevianko, A.P., Fedeneva, I.N., Zenin, V.N., 1998. Deposits of Archaeological Site Shestakovo: Preliminary Paleoreconstruction on Pedogenic Features. Palaeoecology of a Pleistocene and Paleolithic Culture of Northern Asia and Adjacent Territories. Institute of Archaeology and Ethnography Russian Academy of Sciences Siberian Branch, Novosibirsk, pp. 135e143 (in Russian). Derevianko, A.P., Zenin, V.N., Leshchinsky, S.V., Mashchenko, E.N., 2000a. Peculiarities of mammoth accumulation at Shestakovo site in West Siberia. Archaeology, Ethnology, and Anthropology of Eurasia 1 (3), 42e55. Derevianko, A.P., Zenin, V.N., Fedeneva, I.N., 2000b. Some Results of Pedogenic Signs Studying in Deposits of Shestakovo Site (On Materials of 1999). Problems of Archeology, Ethnography, Anthropology of Siberia and Adjacent Territories. Institute of Archaeology and Ethnography Russian Academy of Sciences Siberian Branch, Novosibirsk 4, pp. 41e45 (in Russian).
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Derevianko, A.P., Fedeneva, I.N., Zenin, V.N., 2002. Bioclimatic Conditions of Formation of Shestakovo Site Deposits (Western Siberia). Main Regularities of Global and Regional Climate Changes and Environment in the Late Cenozoic of Siberia. Institute of Archaeology and Ethnography Russian Academy of Sciences Siberian Branch, Novosibirsk, pp. 150e156 (in Russian). Dobrovolckiy, G., Dergacheva, M., 2012. Paleosols, Environment and Their Diagnosis Method. Institute of Soil Science and Agrochemistry Russian Academy of Sciences Siberian Branch, Novosibirsk, 264 p. (in Russian). Fedeneva, I.N., 2003. Pedogenic Features of Shestakovo Site Deposits and Evolution of Soil-forming Conditions Shestakovo Upper Paleolithic Site. Institute of Archaeology and Ethnography, Supplement, Novosibirsk, pp. 137e143 (in Russian). Fedeneva, I.N., Dergacheva, M.I., 2003. Paleosols and environmental reconstruction in Altai mountainous areas. Quaternary International 106107, 89e101. Fedeneva, I.N., Dergacheva, M.I., 2006. Soilscape evolution of West Tien Shan during the Late Pleistocene based on humus properties of the Obi-Rakhmat archaeological site. Quaternary International 156157, 60e69. Fedeneva, I.N., Zenin, V.N., Borisov, M.A., 2000. Evolution of Soil Formation Processes in Sartan Time in South of West Siberian Lowland in Connection with Climate Fluctuations//Modern Problems of Soil Science in Siberia. Tomsk State University, Tomsk, pp. 204e207 (in Russian). Handbook of climate of the USSR, 1965. Gidrometeoizdat, Leningrad, 20. Part 25. (in Russian). Khmelev, V.A., 1989. Loessy Chernozems of Western Siberia. Nauka, Novosibirsk, 201 p. (in Russian). Kuzmin, Y.V., Orlova, L.A., Zolnikov, I.D., Igolnikov, A.E., 2000. The history of mammoth (Mammuthus primigenius Blum.) population in Siberia and adjacent areas (based on radiocarbon data). Russian Geology and Geophysics 41, 746e754. Kuzmin, Y.V., Orlova, L.A., Stuart, A.J., Zenin, V.N., Dementiev, N.L., 2001. Humanmammoth (Mammuthus primigenius Blumenbach) inter-relationships in the Palaeolithic of Siberia: a review of current knowledge. In: The World of Elephants: Proceedings of the 1st International Congress, Rome, pp. 714e717. Leschinsky, S.V., 1998. Paleoecology of the Pleistocene and Stone Age Cultures of Northern Asia and Adjacent Territories. Institute of Archaeology and Ethnography Press, Novosibirsk, pp. 209e220 (in Russian). Leschinsky, S.V., Zenin, V.N., Mashchenko, E.N., 2003. The Nature Accumulation of Ivorys Mammoth at Shestakovo Site. Paleogeography of the Stone Age. Publishing RIO KGPU, Krasnoyarsk, pp. 59e60 (in Russian). Lopatin, V.N., Mashchenko, E.N., Tarasenko, K.K., Podlesnov, A.V., Demidenko, N.V., Kuzmin, E.A., 2015. A unique burial site of early Cretaceous vertebrates in Western Siberia (the Shestakovo 3 locality, Kemerovo Province, Russia). Doklady Biological Sciences 462, 148e151 (in Russian). Orlov, D.S., 1990. Humic Acid of Soils and General Theory of Humification. Moscow State University Press, Moscow, 325 p (in Russian). Ponomareva, V.V., Plotnikova, T.A., 1980. Humus and soil forming. Leningrad, Nauka, 221 p (in Russian). Trofimov, S.S., 1975. Soil Ecology and Soil Resources of Kemerovo Region. Nauka. Siberian Branch, Novosibirsk, 300 p. (in Russian). Vasil'ev, S.A., 2001. Man and Mammoth in Pleistocene Siberia. In: The World of Elephants International Congress, Rome, pp. 363e366. Vasil'ev, S.A., Kuzmin, Y.V., Orlova, L.A., Dementiev, V.N., 2002. Radiocarbon-based chronology of the Paleolithic in Siberia and its relevance to the peopling of the new world. Radiocarbon 44, 503e530. Welte, Е., 1955. Neuere Ergebnisse der Humusforschung. Angewandte Chemie 67 (5), 67e71. Zenin, V.N., 2002. Major stages in the human occupation of the West Siberian plain during the Paleolithic. Archaeology, Ethnology and Anthropology of Eurasia 4, 22e44 (in Russian). Zenin, V.N., Plicht, J.V.D., Orlova, L.A., Kuzmin, Y.V., Brantingham, P.J., 2000a. Geoarchaeology of the Shestakovo Upper Paleolithic site, Western Siberia: Humanmammoth interactions during the Last Glacial Maximum. Current Research in the Pleistocene 17, 103e105. Zenin, V.N., Plicht, J.V.D., Orlova, L.A., Kuzmin, Y.V., 2000b. AMS 14C chronology of woolly mammoth (Mammuthus primigenius Blum.) remains from the Shestakovo upper Paleolithic site, western Siberia: timing of human mammoth interaction. Nuclear Instruments and Methods in Physics Research 172, 745e750.
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Shestakovo site of Western Siberia (Russia): Pedogenic features, humic substances and paleoenvironment reconstructions for last 20e25 ka Maria Dergacheva a, b, *, Irina Fedeneva a, Natalia Bazhina a, Olga Nekrasova c, Vasiliy Zenin b a
Institute of Soil Science and Agrochemistry of Siberian Branch of Russian Academy of Sciences, Av. of Academician Lavrentiev 8/2, 630090 Novosibirsk, Russia Institute of Archaeology and Ethnography of Siberian Branch of Russian Academy of Sciences, Av. of Academician Lavrentiev 17, 630090 Novosibirsk, Russia c Ural Federal University named after the First President of Russia B. N. Yeltsin, Lenina St. 51, 620000 Yekaterinburg, Russia b
a r t i c l e i n f o
a b s t r a c t
Article history: Available online xxx
New data characterizing sediments of the Shestakovo-III section located in the southern part of the West Siberian plain have been obtained. The section reveals 9 m of strata in which a number of paleosols and pedogenic zones are identified on the basis of cumulative features of pedogenesis. Paleosols and pedogenic features reflect the pedogenic transformation of sediments in different environments during the late Karghinsk interval (W2), Sartan Glaciation (W3) and Holocene period. The lower part of the sediments at a depth of 7.5e8.5 m has radiocarbon dates from 25 to 18,000 years. The obtained characteristics of the composition, structure and properties of humic substances, as well as comparison with data obtained earlier by other methods of environmental reconstruction enable recognition of the environment at the southern margin of the West Siberia Plain during the last 20e25 ka in more detail. © 2015 Elsevier Ltd and INQUA. All rights reserved.
Keywords: Pedogenic features Pedohumus method Paleoenvironment Late Pleistocene Holocene Western Siberia
1. Introduction The Shestakovo site is widely known in connection with the findings of bones and complete skeletons of dinosaurs and other fauna of the Cretaceous period (Averianov et al., 2002; Leschinsky et al., 2003; Lopatin et al., 2015). It is also known for a cluster of mammoth fauna associated with archeological artefacts of Paleolithic age (Derevianko et al., 2000a,b; Zenin et al., 2000a; Zenin, 2002). However, the site is extremely interesting from the points of view of paleogeography and stratigraphy. The upper part of these deposits is related to Sartan glaciations and Holocene time. The great thickness of this part of strata and their almost undisturbed state allow tracking directions of paleoecological changes in detail, revealing even relatively short cold and warm periods. Deposits of the Shestakovo site have attracted attention of research of different scientific directions (Leschinsky, 1998; Derevianko et al., 1998, 2000a,b, 2002; Zenin et al., 2000a, b;
* Corresponding author. Institute of Soil Science and Agrochemistry of Siberian Branch of Russian Academy of Sciences, Lavrentieva St. 8, 630090 Novosibirsk, Russia. E-mail address: [email protected] (M. Dergacheva).
Kuzmin et al., 2000, 2001; Fedeneva et al., 2000; Vasil'ev, 2001; Vasil'ev et al., 2002; Fedeneva, 2003). Publications include the stratigraphy of the Shestakovo site, radiocarbon data, sporo-pollen spectra of single stratigraphic layers, finds of Mammoth bones, and data of archaeological investigations. The composition of these deposits has been studied and paleoecological conditions have been discussed. This information has been published only in Russian (Fedeneva et al., 2000; Fedeneva, 2003). The direction of the paleoenvironmental change during the period of deposit formation in the Shestakovo-III section has been established (Fedeneva, 2003). The lower part of deposits that, according to the published radiocarbon dates (Derevianko et al., 2000a,b), corresponds to the end of the Karginsk interval and the beginning of the Sartan cryochron was generated in the southern taiga and (or) northern forest-steppe. During the Sartan cryochron, three stages of glacier activation divided by warmer stages have been identified. In this period the landscapes varied from tundra to southern taiga. During the Holocene optimum, the characteristics of the environment were consistent with the conditions of steppe and were warmer than in modern times. Thus, the general trend of the environment change in the last 20e25 ka in southern West Siberia based on some pedogenic
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features of deposits has been revealed. This trend does not contradict the reconstructions based on other methods of paleogeography (Derevianko et al., 2000a,b; Zenin et al., 2000a,b), but it includes the characteristics of only relatively long stages of paleogeographical history of this period. However, the need to reduce the step on the time scale in solving various problems of stratigraphy and paleogeography is obvious. Application of the pedohumus method of paleoenvironmental diagnosis (Dergacheva, 1997, 1998a,b, 2003, 2008, 2012) allows for a more detailed reconstruction of the changes in the natural conditions and climate than is possible using the traditional set of pedogenesis features (particle size distribution changes with depth TOC pH, CaCO3 and other characteristics of the material composition of deposits). Recently, the team of authors has obtained new data on the Shestakovo site deposits that characterize them from the viewpoint of paleopedogenesis. Products of organo-mineral interaction such as humic acids and their ratios with other components of humus substances have been studied. It is this combination of pedogenic features that forms the basis of the pedohumus method. The purpose of this paper is to present the reconstruction of the environment during the last 20e25 ka based composition, structure, and properties of humic acids as well as their ratio with other components of humus.
constitutes the orographic barrier for humid air masses coming from the north-west and south-west. This leads to the presence of areas with individual climate characteristics and complex alternation of steppe and forest-steppe, and taiga landscapes (Agroclimatic resources …, 1973; Trofimov, 1975). The climate of the study area has the following quantitative parameters: average temperature is 0.3 C, the average July temperature is þ18 C, in January 18 C; the sum of active air temperatures (over þ10 C) is 1700 C per year, and the amount of positive temperatures of 2000e2100 C; the average annual temperature of the soil surface is not more than 1 C, negative temperatures penetrate to a depth of about 1 m; prevailing winds are southwest; annual precipitation 420e470 mm with minimum during the summer months; the air humidity varies between 75 and 80%; and snow depth is not more than 0.5 m (Handbook of climate …, 1965). Leached and podzolized chernozems (Haplic Сhernozems and Luvic Phaeozems) are predominant soils in the study area. They are characterized by a considerable thick humus horizon with a high accumulation of total organic carbon (TOC), good structure, heavy texture, neutral-slightly alkaline reaction (pH 7e8), the prevalence of calcium in the soil absorbing complex and the presence of carbonates in the lower horizons of the soil profile (Trofimov, 1975; Khmelev, 1989).
2. Objects and methods
2.2. Objects of investigation
2.1. Regions studied
The Shestakovo site deposits represent the end of Karginsk interval (W2), Sartan Glacial (W3), and Holocene. This is confirmed by published radiocarbon dates for the lower part of the section obtained on the basis of animal bones (Derevianko et al., 2000a,b; Zenin et al., 2000b) and by the AMS date of 4857 ± 87 NSKA GA 3854 at a depth of 120e130 cm on deposits of the Holocene optimum. Deposits of the Shestakovo site were exposed in the section Shestakovo-III and by a series of additional sections and were previously described in detail from positions of stratigraphy and archaeological stratification (Leschinsky, 1998; Derevianko et al., 2000a,b). The Shestakovo-III section exposes 9 m of sediments in total. The sediments cover the period from 25 ka up to present time. Thirteen stratigraphic layers were distinguished in the sediments, which from the archaeology standpoint were stratified into 25 layers (layer 21 in the Shestakovo-III section sediments was absent) (Fig. 2). Section III revealed the following sequence of layers (description is given from the viewpoint of morphological reflection of pedogenic processes; with depths in a sampling place measured from the surface). Layer 1 (0e0.25 m). Humus horizon of modern arable leached chernozem (Huplic Chernozem). In the upper part is lighter-gray with brownish tinge (10 YR 6/1), in lower e dark gray with a brownish tinge (10 YR 4/1); fine angular blocky-granular structure, clay loam, compact, with abundance of roots; gradual transition to an underlying layer, boundary is smooth. Layer 2 (0.25e0.60 m). It is a little lighter than overlying layer: light gray with brownish tinge (10 YR 5/1), fine angular blockygranular structure, clay loam, compact (a little more compact in comparison with layer 1); with abundance of roots; gradual transition, boundary is smooth. Layer 3 (0.60e0.90 m). Light-brown with gray tinge (7.5 YR 7/1); with nutty subangular blocky-granular structure, loam (clay loam), rather compact; with abundance of roots; abrupt transition, boundary is smooth. Layer 4 (0.90e2.15 m). Includes the dual Holocene pedocomplex. The upper paleosol is presented by the humus horizon (A)' (dark gray Y 5/1, uniform in color, loam, with angular blocky-nutty structure, compact) and subhorizon (AB)' (dark gray with brown
The Shestakovo site is situated on the right bank of the Kiya River in Kemerovo Region (55 540 N. 87 570 W) on southern margins of the West-Siberian Lowland (Fig. 1). The area under research is on a very weakly undulated flat plain with altitudes 150e200 m a.s,l. Watershed areas are broken by shallow ravines and valleys of small brooks and rivers. The Shestakovo location belongs to the zone of “insular” forest steppe. Kemerovo Region is located in the center of the Asian continent and is characterized by extreme continental climate. The region also has specific climatic features due to relief. A mountain system
Fig. 1. Location of the Shestakovo site (according to Derevianko et al. (2000a) with changes).
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Fig. 2. . Deposits of the Shestakovo-III section (according to Derevianko et al (2000a) with changes).
tinge 10 YR 4/1), loam, with nutty subangular blocky structure, compact). In the lower paleosol remained the humus horizon (A)'' (dark gray with weak brownish tinge 10 YR 5/1, loam (clay loam), with coarse blocky structure), horizon (B)'' (light brown 10 YR 5/ 4) clay loam, rather compact, with nutty subangular blocky structure) and horizon (BC)'' (pale-yellow 5 Y 6/4) clay loam, compact, with nutty structure, fissured, with accumulation of carbonates (pseudomicellia); flow of humus matter on the courses of roots). Layer 5 (2.15e2.83 m). Alternation of sandy, sandy loam and loam sublayers; sandy sublayers are 2e5 cm, loam sublayers e 1e1.5 cm (in the upper part of the layer more thick, to 8 cm, sandy loam sublayer is allocated). The general color is pale-yellow (5 Y 6/ 4), sandy sublayers are a little darker. Loam deposits have nutty subangular blocky structure, with carbonate pseudomicellia. In the lower part of the layer there are grey tones, iron spots and darker (dark-brown) sublayers. Gradual transition, boundary is smooth. Layer 6 (2.83e2.95 m). Variously colored e pale-yellow clay with dark-brown (5 Y 5/4) loamy sublayers and lens, with nutty subangular blocky structure, porous, compact, courses of roots, carbonate pseudomicellia, iron spots are noticeable; gradual transition to underlying layer, boundary is smooth.
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Layer 7 (2.95e3.48 m). Pale-yellow with dark-brown tinge (5 Y 5/4), loam clay, with nutty-blocky structure, porous; compact, fissured; courses of roots are noticeable, in the upper part of the layer e carbonate pseudomicellia; gradual transition to an underlying layer, boundary is smooth. Layer 8 (3.48e3.93 m). Dark-pale-yellow (5 Y 5/4), clay loam (clay), with nutty (nutty-blocky) structure; compact, ductile; abundant manganese spots, roots, rare pseudomicellia; transition to an underlying layer is abrupt, boundary is irregular. Layer 9 (3.93e4.41 m). The main color is pale-yellow (5 Y 6/4), brown e dark-brown sublayers are noticeable, clay loam, with nutty subangular blocky; pseudomicellia is noticeable only in darkcolored sublayers; rather compact; rare manganese spots e in the upper part of the layer; gradual transition to an underlying layer, boundary is smooth. Layer 10 (4.41e4.88 m). Light-pale-yellow (5 Y 8/4), more uniform in coloring, than layer 9; clay loam, with nutty-blocky structure; rather compact; rare manganese and carbonate spots, lightbrown spots (to 3e5 mm); the lower boundary is irregular, with wedges 5e6 cm, transition is abrupt. Layer 11 (4.88e6.03 m). Pale-yellow (5 Y 6/4), variously colored, in the lower part of the layer there are gray tone in coloring, lightbrown thin sublayers with not clear borders; loam clay, with nutty subangular blocky structure, on sides of particles iron spots are noticeable; rather compact, fissured; carbonate pseudomicellia, manganese spots are noticeable; the lower boundary is irregular, with wedges 5e6 cm, transition is abrupt. Layer 12 (6.03e7.22 m). Variously colored, the main color is dark-pale-yellow (5 Y 4/4) with alternation of more and less darkcolored sublayers (light-pale-yellow (5 Y 8/4), pale-yellow (5 Y 6/4), dark-pale-yellow (5 Y 4/4), in the lower part of the layer there are gray tone in coloring; with nutty subangular blocky structure, loam; rather compact, manganese and iron spots and rusty sublayers are noticeable; the lower boundary is wavy and transition e gradual. Layer 13 (7.22e7.31 m). Pale-yellow (5 Y 6/4), loam, with nutty subangular blocky structure; compact; thin sandy (or sandy loam) sublayers are noticeable; rare manganese spots; transition is gradual. Layer 14 (7.31e7.45 m). Similar in morphological properties to layer 13, differs in higher quantity of small particles (loam clay); the lower boundary is wavy, crumpled and transition is abrupt on coloring. Layer 15 (7.45e7.59 m). Light gray with brown tinge (10 YR 5/1), clay; angular block-granular structure; rather compact; the lower boundary is wavy. Layer 16 (7.59e7.79 m). Dark-pale-yellow with brown tinge (5 Y 4/3), uniform in color, loam, with nutty subangular blocky structure; rather compact; rare sandy lenses, manganese spots, carbonate pseudomicellia are noticeable; gradual transition, boundary is smooth. Layer 17 (7.79e7.88 m). Differs from layer 16 in lighter color e pale-yellow with a brownish tinge (5 Y 6/3), according to other morphological characteristics it is similar to layer 16. Layer 18 (7.88e7.98 m). Dark-pale-yellow, loam, with nutty subangular blocky structure; less dense in comparison with layers 16e17; rare manganese spots; smooth boundary and abrupt transition. Layer 19 (7.98e8.08 m). Dark-pale-yellow (5 Y 4/3), loam clay, with nutty-blocky structure, compact; abundant manganese spots; gradual transition. Layer 20 (8.08e8.18 m). Differs from layer 19 in the large amount of manganese spots; the lower boundary is wavy and transition is abrupt.
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Layer 22 (8.18e8.34 m). Light-pale-yellow (5 Y 8/4), in middle part quite thick rusty crumpled sublayer is noticeable; loam clay, with nutty-blocky structure, compact; gradual transition to underlying layer, boundary is wavy. Layer 23 (8.34e8.64 m). Dark-pale-yellow (5 Y 4/4), loam, with nutty-blocky structure, rather compact; rare manganese and iron spots, carbonate pseudomicellia. Layer 24 (8.64e8.79 m). Differs from layer 23 in the large number of manganese spots; gradual transition to underlying layer, wavy lower boundary. Layer 25 (8.79e8.96 m). It is similar on properties to overlying layers; gray tones (5 Y 5/1), sandy loam. Thus, morphologically deposits of the Shestakovo-III section are layered sediments, non-uniform in color, particle size distribution, structure, density, presence of impurities, and pedogenic transformation degree.
2.3. Methods of analyses Ninety-eight samples were taken in Shestakovo-III section for analysis. Previously, the following parameters have been measured in these samples (Fedeneva et al., 2000; Fedeneva, 2003): particle size distribution, content of total organic carbon (TOC), carbonates and pH, and humus composition according to the methods of Russian Soil Science adapted to paleosols (Dergacheva, 1984; Dobrovolckiy and Dergacheva, 2012). The study of this section and interpretation of materials obtained from Shestakovo-III deposits were continued from the pedohumus method standpoint. Data characterizing the composition and properties of humic acids and their ratio with other components of humus were obtained. Zones of pedogenesis have been distinguished in the sediments on the basis of data generalizations. A zone of pedogenesis is a layer (horizon) with specific features and differing from over and underlying sediments. The zone is determined by a combination of pedogenic features formed under influence of unidirectional humus- and soil-forming processes. The level of pedogenic features can be different: they can be represented as a full soil profile, as a single diagnostic horizon or their combinations, and morphogenetic or other properties of soil, which are close quantitative parameters. In this work, diagnosis of conditions of paleosol period formation and reconstruction of paleoenvironment for the last 20e25 ka is conducted on the basis of the composition and properties of humic acids and their ratio to fulvic acids. Humic acids were extracted by the standard method. Calcium was removed the humic acids were extracted by 0.1 n NaOH and were precipitated by 2 n HCl. The precipitation was separated by centrifugation, re-dissolved and precipitated by 2 n HCl again. Treatment of humic acids either by 6 n HCl or the mix HCl þ HF for removal of ash elements was not carried out. The share of carbon in elemental composition of humic acids is most closely correlated with temperature conditions, the share of hydrogen is correlated with moisture conditions, and the ratio of these elements (H:C) has a close correlation with all major climatic indices (Dergacheva et al., 2012). The correlation coefficient ranges from 0.75 to 0.98. The element ratio of humic acids, color coefficient Е465:E665 (Welte, 1955) and the ratio of humic acids with fulvic acids are used for revealing paleosol forming conditions. These characteristics are closely correlated with the period of biological activity (PBA). According to Orlov (1990), the PBA duration is equal to the period during which the air temperature is consistently over 10 C and the moisture available is not less than 1e2%.
To visualize the results of the study of the system of paleosol humus substances, the graphic principles described previously (Dergacheva, 1984) have been used. Using humus profilegrams, one can present the features of humus substances composition in the form of areas that give visual representation of the changes of parameters of groups and fractions within the profile and presence of uniform and different thicknesses that can be identified as pedogenic zones. As diagnostics and reconstruction of paleoenvironment in this article are carried out using the pedohumus method, we briefly describe the most important of its provisions by which it is possible to use it as an independent method of paleogeography similar to the method of sporo-pollen analysis. First at all, the composition and properties of humic acids, as well as their ratio to the other components of humus substances, are caused by the specific conditions (the combination of temperature and humidity) in the place where they were formed (Dergacheva, 1997, 2008). Humic acids are accumulative component humus and they almost do not migrate. In addition, humic acids, as well as aggregate of humus substances, are self-regulating systems that can maintain status acquired during their formation (Dergacheva, 1989). The share of carbon in the humic acids of soils and paleosols depends on the zonal natural conditions and the continental climate. Key indicators of the elemental composition of humic acids paleosols do not depend on their age. They are caused by climate. Humic acids preserve of some properties in diagenesis during Pleistocene-Holocene period (Dergacheva et al., 2000, 2012). A detailed description of the method has a number of works only in Russian (Dergacheva, 1997, 1998a,b; 2008, 2011, 2012). The principles of the method and also the diagnostics and reconstruction paleoenvironment based for this method have been published in English as well (Dergacheva, 1998a, 2013, 2003; Fedeneva and Dergacheva, 2003, 2006; Dergacheva et al., 2012). 3. Results of investigation and their interpretation It has been shown (Fedeneva, 2003) that the mineral part of deposits transformed by a pedogenic processes is relatively monotonous especially in the lower part from 6 to 9 m. The greatest variation has been found in sand particles (Fig. 3). According to data (Fig. 3), the entire thickness of sediments is rich in calcium carbonate, varyimg mostly between 5 and 8% by weight of fine earth. Very high accumulation of calcium carbonate is found only in sediments associated with the humus layer of the Holocene optimum at the depth of 178e215 cm. While the mineral part of deposits is relatively monotonous, the quantitative and qualitative characteristics of organic matter vary in thickness substantially (Fig. 4). The content of organic carbon throughout the section, except for profiles of the modern soil and paleosol of Holocene optimum is less 0.3% of fine deposit mass (Fig. 4, a). The distribution of organic carbon throughout the section makes it possible to distinguish layers of relative humus accumulation. These layers are also characterized by increase in both the share of humic acids and in the carbon ratio of humic and fulvic acids (Cha:Cfa) (Fig. 4, b, i). Fulvic acids, as a rule, are prevailing forms among humus substances (Fig. 4, b). In some cases non-hydrolyzed forms of humus (humins) are dominant (Fig. 4, d). The content of humic acids reaches 30e40% in some layers (Fig. 4, b), that for paleosols and deposits of Late Neopleistocene can be estimated as relativity high (Dergacheva and Zykina, 1988). Calcium humates prevail among humic compounds (Fig. 4, f). Humic acids associated with clay minerals are in insignificant quantities. In some layers this form of humus substances is in trace quantities or is absent. The quantity of free fulvic acids
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Fig. 3. General characteristics of the deposits of the Shestakovo-III section: А e layers; B e particle size distribution (mm): 1e 1e0.25; 2 e 0.25e0.05; 3 e 0.05e0.01; 4 e 0.01e0.005; 5 e 0.005e0.001; 6 e <0.001; C ephysic-chemical properties.
(fraction 1a, according to Ponomareva and Plotnikova, 1980) slightly varies in most deposits, gradually decreasing to the upper 2 m (Fig. 4, h). Features of structure and properties of humic acids (H:C, C:N, E465:E650) also significantly vary in deposits, reflecting relative changes of the environment (Fig. 5, d, e, f). In deposits of the lower part of the section (from 9 to 7 m), the H:C ratio is within the range 1.3e1.4 (approximately), and nitrogen saturation of humic acids (C:N ratio) in the most cases is more than 14e15, being reduced to 11e12 in the upper part of the section. The value of the E465:E650 ratio characterizing complexity of humic acid structure (i.e., the ratio of their shears between the peripheral and so-called nuclear parts) is specific for the modern soils formed in humid conditions. The deposits correlating with the Sartan period of the Late Pleistocene differ in alternation of values of both H:C ratios in
humic acids and E465: E650. In general, their fluctuations are not beyond typical characteristics of HA under humid conditions. These features of HA indicate repeated changes of the relative cooling and warming, against the background of stable temperature conditions changes of humidity. Such specificity of climatic conditions is observed for sediments at a 700e225 cm. In the upper part, the combination of features of humic acids and their ratio to fulvic acids reveal a number of layers with humic acids corresponding to formation in warmer and in less humid conditions (in some cases even arid). The features of humic substances of the Holocene part deposit from 225 cm to the surface reveal a dual pedocomplex of the Holocene optimum and the set of modern soil horizons. The analysis of the set of pedogenic features of Shestakovo section deposits allow us to distinguish a number of pedogenic zones, which characterize different conditions of deposit formation and features of soil forming process (Fig. 5, a, b).
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Fig. 4. Humus profile of the Shestakovo III section deposits: a e TOC, % to soil mass; % to TOC: b e 3; h e FA, fraction 1a; i e Cha:Cfa.
P P HA; c e FA; d e Humin; e e HA, fraction 1; f e HA, fraction 2; g e HA, fraction
Fig. 5. Complex of deposit features of the Shestakovo -III section based on humus substance characteristics (A) and scheme of presence of layers and pedogenic zones (B) a e TOC, % to soil mass; b e magnetic susceptibility, c$105/kg SI; c e Cha:Cfa; Characteristics of humic acids: d e H:C; e e C:N; f e E465:E650.
All deposits were divided into 16 pedogenic zones (the first is in the lower part of Shestakovo section, the 16th e in its upper part). According to data in Figs. 4 and 5, the pedogenic zones have different characteristics. The analysis of quantitative characteristics of the 16 zones of pedogenesis showed that there were numerous changes in bioclimatic conditions over the last 20e25 ka. Diagnostics of pedogenesis conditions have been performed for each of the studied sample, taking into account that the formation of humic acids takes place in accordance with a combination of temperature and moisture; that they are an accumulative component of the soil, and that they are satisfactorily preserved in diagenesis (Dergacheva, 2008). The results were generalized for each zone of pedogenesis. Diagnosis was based on the relationships
between the parameters of humic acids and other humus characteristics of modern soils on the one hand, and with environmental conditions of their formation, on the other. Different indicators of the environmental state are used for this purpose. It is impossible to present the entire volume of diagnosed data and full description of the diagnostic procedure in the given article. We demonstrate the procedure with the example of determination of the period of biological activity, which depends on the combination of heat and moisture. For the analysis of pedogenic zones, the average data for each are used (Fig. 6). This procedure can be performed for the humus horizons or some individual samples depending on the problems being solved. The results demonstrated in Figs. 4e6 and their generalization (Table 1) have revealed the change of periods of
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Fig. 6. Calculation of the periods of biological activity (PBA) of the formation of paleosols and deposits overworked by pedogenesis of Shestakovo-III section using average data for pedogenic zones. IeXVI e pedogenic zones. It is based on the results of studying H:C of humic acids of modern soils formed under varying durations of PBA.
biological activity (PBA) during the formation of the deposits according to each zone of pedogenesis.
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Pedogenic zone II (770e825 cm) differs in the higher amount of organic carbon (0.24 ± 0.02) with small changes in depth, in the higher value of the magnetic susceptibility (1.5e2.0$105/kg), in the tendency to reduction share of humic acids in humus composition to a top of this pedogenic zone, and also slightly in the varying Cha:Cfa, and H:C ratios (0.71 ± 0.08 and 1.36 ± 0.05 respectively). The absolute values of saturation of humic acids by nitrogen and color coefficient tend to decrease. The last parameter has no statistically reliable difference from the previous layer. Sediments in this pedogenic zone were also formed on the background of high humidity, though relatively weaker than zone I. On average, the duration of the PBA is shorter (Fig. 6). Northern taiga replaced southern taiga. Pedogenic zone III includes deposits from 730 to 770 cm. According to the content of organic carbon (0.24 ± 0.03) these deposits does not practically differ from those in the previous zone by the lower content of humic acids, similar content of fulvic acids, significantly lower value of Cha:Cfa (on average 0.58 ± 0.11), similar H:C ratio values (1.37 ± 0.09), and more “mature” humic acid (E4:E6 ¼ 4.11 ± 0.22). During this period, the conditions were almost identical to the previous one. The deposits at the depth of 700e730 cm belong to pedogenic zone IV. This zone is distinguished on the basis of the increased magnetic susceptibility, relatively lower organic carbon content, and Cha:Cfa, and E4:E6 ratios. Its formation proceeded under con-
Table 1 Pedogenic zones of Shestakovo section Pedogenic zone
Depth, cm
TOC, % (average)
I II III IV V VI VII VIII IX X XI XII XIII XIV XV
825e900 770e825 730e770 700e730 595e700 545e595 490e545 425e490 390e425 340e390 275e340 240e275 195e240 140e195 90e140
0.17 0.24 0.24 0.19 0.15 0.18 0.17 0.17 0.16 0.18 0.25 0.12 0.21 0.63 1.90
XVI
0e90
2.17 ± 1.08
a b
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.05 0.02 0.03 0.02 0.01 0.02 0.01 0.02 0.02 0.02 0.03 0.03 0.04 0.33 0.53
Cha:Cfa (average) 0.68 0.71 0.58 0.49 0.34 0.56 0.81 0.60 0.65 0.55 0.93 0.33 0.36 1.06 2.29
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
0.28 0.08 0.11 0.05 0.08 0.14 0.24 0.15 0.19 0.10 0.18 0.07 0.04 0.67 0.36
1.39 ± 0.22
PBA for pedogenic zone, days
Landscape
PBA different landscape conditions, daysb
14
0.05 0.05 0.09 0.04 0.06 0.12 0.10 0.09 0.31 0.07 0.16 0.14 0.09 0.18 0.07
92 87 87 90 119 125 118 119 87 115 100 130 100 150 165
Southern taiga Northern taiga Northern taiga Northern Taiga Southern taiga Forest-steppe Southern taiga Southern taiga Northern taiga Southern taiga Southern taiga Forest-steppe Southern taiga Forest-steppe Steppe
90e120 60e90 60e90 60e90 90e120 120e150 90e120 90e120 60e90 90e120 90e120 120e150 90e120 120e150 150e180
from 18040 ± 175 to 24360 ± 150a
0.84 ± 0.04
150
The southern forest-steppe
150e180
H:C (average) 1.34 1.36 1.37 1.36 1.14 1.09 1.20 1.14 1.37 1.16 1.28 1.02 1.29 0.84 0.71
± ± ± ± ± ± ± ± ± ± ± ± ± ± ±
C dates
For depth 120e130 cm 4857 ± 87 (NSKA GA 3845) Modern period
According to Zenin et al. (2000b) According to Orlov (1990).
The first pedogenic zone is allocated at a depth of 825e900 cm and is characterized by gradual increase of several parameters from the lower part. They are: organic carbon (from 0.07 till 0.21), humic acids (as the tendency) and the value Cha:Cfa (from 0.48 to 1.10), reduction of a share of fulvic acids and saturations of humic acids by nitrogen. Ratios of H:C and E465:E650 (further in the text e E4:E6) change slightly. The first indicator on averages is 1.34 ± 0.05, the second is 4.73 ± 0.13 (Table 1). Here pedogenesis occurred under conditions of high humidity indicated by morphological features listed above, but also by the composition and properties of humic acids with parameters similar to modern soils of humid conditions of formation. The period of biological activity during the formation of the first pedogenic zone could be about 92 days, decreased to 87e90 days in zones IIeIV.
ditions in northern taiga but under relatively higher heat supply and lower humidity. Paleosols and sediments overworked by pedogenesis following pedogenic zones (VeVIII) were formed under more favourable conditions when the PBA varied around 120 days. The fifth zone of pedogenesis at 595e700 cm is characterized by lower values of TOC, magnetic susceptibility, the share of humic acids in the composition of humus substances, and Cha:Cfa value. Indicators H:C and Е4:Е6 point to the beginning of relative warming. The PBA was longer than about 20 days, and met the conditions of the southern taiga. The sixth zone of pedogenesis on the depth 545e595 cm shows further warming reflecting in the transformation of all features of humus in sediments changed by pedogenesis. Humic acids have
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relatively higher proportions of carbon in the elemental composition and the ‘nucleus’ portion in the structural organization. The PBA met the conditions of the forest-steppe (Table 1). The next seventh zone of pedogenesis (490e545 cm) occupies the second half of the eleventh layer and it is characterized by a very low magnetic susceptibility (less than 1.0$105/kg SI) that is specific for this section and by its slight fluctuation, which may indicate the influence of increased humidity. This zone of pedogenesis is very heterogeneous in a number of characteristics. The humic acids and their ratio to fulvic acids correspond to relatively warm and humid conditions. The content of humic acids points to the continuing relative warming that in general is confirmed by the values of H:C and Е4:Е6. The random thin interlayer (probably redeposited) divides these sediments into two parts with similar features. The average values of the composition and properties of humic substances of this zone were calculated without characteristics of this interlayer. The eighth pedogenic zone with thickness of 65 cm (425e360 cm) is close to the previous zone in the total organic carbon content (0.17 ± 0.02), higher magnetic susceptibility (1.12 ± 0.07), the increased amount of fulvic acids in the humus composition, and the value of H:C and Е4:Е6 of humic acids, corresponding to forest conditions with relatively cold and humid conditions. The PBA of this zone is 119 days and is nearly identical to the previous one. Then, there was a reduction of PBA to a minimum of about 87 days that was related with a significant cooling. The ninth zone of pedogenesis (390e425 cm) has low TOC, close to the values Cha:Cfa and Е4:Е6 to those of previous pedogenic zone and reflecting the same conditions. However, the lower ratio of C:N may indicates changes in the vegetation, affecting saturation of humic acid by nitrogen. In this zone, the differentiation of pedogenic characteristics in most strata is observed: the share of humic acids increases and fulvic acids decreases, and the absolute values Cha:Cfa increase from bottom to top. In accordance with these facts, the ratio of H:C is gradually lowered. In general, the sediments of this pedogenic zone correspond to relatively colder formation conditions than in the previous case. During the formation of the next pedogenic zone the PBA increased to 115 days, then during the formation of XI and XIII zones it was about 100 days, and during XII zone about 130 days. The tenth zone of pedogenesis includes deposits with thickness of 50 cm (from depth of 340 cm) with low TOC, low magnetic susceptibility and characteristics of humic acids corresponding to the southern forest type The higher amount of total organic carbon is observed in sediments of the eleventh pedogenic zone, but the combination of different features of the composition and properties of humic acids and their correlation with fulvic acids is variable. The interlayers with characteristics reflecting relatively warmer or colder wet conditions of pedogenesis alternate. The relative warming is reflected in the characteristics of sediments of the next, XII zone of pedogenesis, which is a dual pedocomplex consisting of superimposed paleosols. Probably rare and low-power lithogenesis dominated in this period, which was followed by transformation of soil formation processes. Both paleosols are very thin (no more than 15e20 cm), but the parameters of their humus horizons correspond to overall warming of the climate. The deposits of this zone were formed in forest-steppe. Properties of the pedogenic zone XIII reflect the next phase, which terminates the Sartan period. The following two zones of pedogenesis at the depth of 90e195 cm are the profiles of paleosols formed under warmest conditions. The value of PBA reflects the fact that this pedogenic zone was formed under southern taiga conditions. The upper of these zones was formed as the result of a rare
but powerful lithogenesis and its subsequent pedogenic transformation. The highest period of biological activity was during the formation of the upper paleosols of the pedocomplex of Holocene optimum. The conditions of formation of humus and soils were favorable and characterized by the highest PBA duration of 165 days. The durations of PBA of the lower paleosol of this pedocomplex and modern soil are almost identical. The humus horizon of the paleosol formed in warmer and drier conditions. In zone XIV at the depth of 140e195 cm is a chernozem paleosol with typical change in TOC with depth, change in the magnetic susceptibility, and the shares of humic acids and fulvic acids. The former decrease with depth, the latter increase, and characteristics of humic acids correspond to the level of the steppe soil. This soil is clearly differentiated into horizons (A), (AB) and (B) in all respects. There is another paleosol characterized as a zone XV. It was formed in steppe conditions and is differentiated into two horizons, (A) and (AB). Characteristics of humic acids correspond to steppe soils with different degrees of humidity. The zone of pedogenesis XVI has a thickness of 90 cm, has the horizons A, AB and B in this section, and corresponds to all the quantitative parameters of a Chernozem formed in the southern part of forest-steppe. Thus, one can diagnose the paleoenvironment with any step of timeline, with any amount and location of samples, conduct neighboring correlations, and compare identified general trends of changes in the environment of local areas. Instead of the H:C ratio and the relationship of this characteristic of humus composition with PBA, it is possible to use any indicator of composition, structure and properties of humic acids that is specific to the conditions of the environment and preserves their specificity in diagenesis. Any indicators of climate, vegetation, or relief can also be used in that case, if the current relationships are already identified. 4. Conclusion The approaches of pedohumus method to paleosol diagnostics and paleoreconstruction allowed detailed paleoenvironment reconstructions of the end of the Karginsk interstadial, the Sartan glacial period and the Holocene. A number of bioclimatic condition fluctuations caused by local specificity of the climate was revealed. It has been established that the lower part of the deposits formed in the final stages of the Karginsk interval or at the beginning of the Sartan period corresponds to conditions of taiga landscapes. The deposits of several pedogenic zones correspond to forest-steppe landscapes. The stages of glacier activation are distinguished during the Sartan period, which were interrupted by relatively warm stages. The landscapes varied in the range from northern taiga to forest-steppe within this period. The most prominent event of the Holocene was the climatic optimum during which a paleosol of chernozem type was formed and the environment corresponded to steppe conditions favourable for soil formation. Diagnostics conducted by pedohumus method does not contradict data obtained by palynological and other paleogeography methods (Derevianko et al., 2000a,b). The obtained characteristics of the composition, structure and properties of humic substances, as well as comparing the results of environment reconstruction by other methods have allowed us to carry out more detailed environment diagnosis of the last 20e25 ka on the West Siberian Plain's southern edge. Moreover, they have illustrated the reliability of information preserved in humic acid features. The formation of the deposits of the Shestakovo-III section happened during a change from frequent but weak lithogenesis to rare and weak and then (approximately from the depth of 225 cm) rare and powerful lithogenesis.
Please cite this article in press as: Dergacheva, M., et al., Shestakovo site of Western Siberia (Russia): Pedogenic features, humic substances and paleoenvironment reconstructions for last 20e25 ka, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.10.087
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Please cite this article in press as: Dergacheva, M., et al., Shestakovo site of Western Siberia (Russia): Pedogenic features, humic substances and paleoenvironment reconstructions for last 20e25 ka, Quaternary International (2015), http://dx.doi.org/10.1016/j.quaint.2015.10.087